Ethylene polymerization with catalyst of nickel oxide on carbon plus alkaline earth metal



United States Patent ETHYLENE POLYMERIZATION WITH CATALYST OF NICKELOXIDE 0N CARBQ'N PLUS ALKA- LINE EARTH METAL Morris Feller, Park Forest,and Edmund Field, Chicago, Ill., assignors to Standard Oil Company,Chicago, 11]., a corporation of Indiana N0 Drawing. Application March30, 1954, Serial No. 419,916

15 Claims. (Cl. 260-943) This invention relates to a process for theconversion of ethylene to normally solid resinous, wax-like andgrease-like hydrocarbon products by contact with an alkaline earth metaland a catalyst comprising essentially nickel oxide extended on an activecarbon such as an active coconut charcoal.

One object of our invention is to provide novel and highly usefulcatalysts for the preparation of high molecular weight polymers fromethylene-containing gas mixtures. Another object is to provide arelatively lowtemperature, low-pressure process for the conversion ofethylene in substantial yields into high molecular weight normally solidpolymers having molecular weights ranging upwardly from 300. These andother objects of our invention will become apparent from the followingdescription thereof.

Briefly, the inventive process comprises the conversion of ethylene insubstantial yields to high molecular weight polymers having a molecularweight of at least 300 and including grease-like, wax-like and tough,resinous ethylene polymers, by contacting ethylene with calcium or otheralkaline earth metals and a solid catalyst comprising essentially anickel oxide-activated carbon containing a minor proportion, usuallybetween about 0.1 and about weight percent, of nickel oxide (calculatedas nickel) and a major proportion of activated carbon, preferably acoconut charcoal. The catalyst will be hereinafter referred to as thenickel catalyst. The contacting of ethylene, nickel catalyst andalkaline earth metal is effected at temperatures within the range ofabout C. to about 250 C. It is highly desirable to supply to thereaction zone a liquid medium which serves both as a reaction medium anda solvent for the solid reaction products. Suitable liquid reactionmedia for polymerization include various hydrocarbons, particularly anaromatic hydrocarbon such as benzene, toluene or xylenes. The conversionof ethylene can be effected in the absence of a liquid reaction mediumor solvent and the catalyst containing accumulated solid polymericconversion products can be treated from time to time, within or outsidethe conversion zone, to effect removal of conversion products therefromand, if necessary, reactivation or regeneration of the catalyst forfurther use. The ethylene partial pressure in the reaction zone can bevaried between about atmospheric pressure and 15,000 p. s. i. g. or evenhigher pressures, but is usually effected at pressures between about 200and 5000 p. s. i., or most often at about 1000 p. s. i.

The practice of the process of the present invention leads to ethylenepolymers of widely variant molecular weight ranges and attendantphysical and mechanical properties, dependent upon the selection ofoperating conditions. The inventive process is characterized by extremeflexibility both as regards operating conditions and as regards theproducts producible thereby. Thus the present process can be effectedover extremely broad rangesnof temperature and pressure. The practice ofthe present process can lead to grease-like ethylene homopolymers havingan approximate molecular weight range of 300 to 700, wax-like ethylenehomopoly-mers having an approximate specific viscosity (X10 betweenabout 1000 and 10,000, and tough, resinous ethylene homopolymers havingan approximate specific viscosity (X10 of 10,000 to more than 300,000[(9 relative -l) l0 By the term tough, resinous polyethylene as usedherein, we mean polymer having a brittle point below 50 C. (A. S. T. M.Method D746-51T), impact strength greater than two foot pounds per inchof notch (A. S. T. M. Method D256-47T-Izod machine) and minimumelongation at room temperature (25 C.) of

Other reactive materials may be added to ethylene, particularlypropylene or other m'ono-olefinic hydrocarbons such as n-butylenes,isobutylenes, t-butylethylene; acetylene, butadiene, isoprene, and thelike, usually in proportions between about 1 and about 25% by weight,based on the weight of ethylene.

An important feature of the present-invention is employment of analkaline earth metal, viz. beryllium, magnesium, calcium, strontium -orbarium. We may employ mixtures of the alkaline earth metals or alloyscomprising alkaline earth metals. The inclusion of the alkaline earthmetal with a nickel catalyst results in increased yields of solidpolymers of ethylene. The nickel catalyst, when employed with calcium orother alkaline earth metal, functions well in the presence of largeproportions of liquid reaction medium, the life of the nickelpolymerization catalyst is extended and polymers having desirable rangesof physical and chemical properties can be readily produced.

The proportion of calcium or other alkaline earth metal promoteremployed in our process can be varied from about 0.01 to about 10 partsby weight per part by Weight of nickel catalyst (total weight of solidcatalyst). Usually calcium is employed in proportions between about 0.5and about 2.0 parts by weight per part by weight of the nickel catalyst.The optimum proportions can readily be determined in specific instances,by simple small-scale tests with the specific feed stocks, liquidreaction medium, reaction mediumzcatalyst ratio, catalyst, temperature,pressure and nature of the product which is desired.

The nickel component of the catalyst is extended upon a major proportionof an activated carbon. Thus, we may employ activated charcoals derivedfrom cellulosic materials, particularly coconut, having surface areasbetween about 700 .and about 1200 square meters per gram, pore volumesof about 0.53 to 0.58 cc. per gram and pore diameters of about 20 to 30A., and, in some instances, small amounts of combined oxygen. Theactivated charcoal or other carbon support may be pretreated with nitricacid before use as a catalyst support in order to remove basicmaterials, for example, as described in E. F. Peters application forUnited States Letters Patent, Serial No. 164,825, filed May 27, 1950,now U. S. Patent 2, 692,295.

The preparation of nickel catalysts supported upon activated carbon,particularly coconut charcoal, is well known in the art and thepreparative methods form no part of the present invention. Usually weprefer to prepare the catalyst by a cheap, simple and efficacioustechnique, which is described briefly hereinafter.

A suitable method of catalyst preparation involves absorbing nickelnitrate from an aqueous solution upon a porous active carbon such as asuitable charcoal in an amount sufficient to produce the desired nickelcontent in the finished catalyst. The charcoal containing absorbednickel salt is then treated thermally at temperatures between about 200and about 350 C. to effect decomposition of nickel nitrate to formnickel oxide, suitably by heating under a partial vacuum such as 1 to 20mm. of

mercury (absolute pressure) or in the presence of steam or by theapplication of heat, vacuum and steam, as is known in the art. Theresultant catalyst comprises principally nickel oxide extended uponcharcoal.

Although the nickel catalyst may contain between about 0.1 and about 20weight percent of nickel (calculated as metallic nickel), we usuallyemploy catalyst containing between about 3 and about weight percent ofnickel.

The activated carbon support seems to play a unique role in thecatalyst. Other supports which might be considered prima facieequivalents, greatly reduce or virtually destroy the power of thecatalyst to produce solid polymers from ethylene, vis. alumina andsilica supports such as kieselguhr.

If it is desired to employ the nickel catalyst in the form of pelletslarge enough to be retained on a -mesh sieve or at least about 0.1 inchin the largest dimension, it is desirable to pellet the nickel catalystwith between about and about weight percent, based on the total weightof the pellet, of a diflicultly reducible metal oxide filler materialsuch as alumina, titania, zirconia or silica.

The nickel catalyst can be employed in various forms and sizes, e. g.,as powder, granules, microspheres, broken filter cake, lumps, or shapedpellets. A convenient form in which the catalysts may be employed is asgranules of about 20l00 mesh/inch size range.

Although ethylene may be polymerized to produce normally solid polymersin the presence of alkaline earth metal-nickel oxide-charcoal catalystseven at room temperature, we prefer to employ temperatures between about75 C. and about C.

Reaction pressures may be varied within the range of about 15 p. s. i.ethylene partial pressure to the'maximum ethylene partial pressure whichcan economically be employed in suitable commercial equipment, forexample up to as much as 30,000 p. s. i. A convenient ethylene partialpressure range for the manufacture of solid polymers by the use of thepresent catalyst is about 200 to about 5000 p. s. i., which constitutesa distinct advantage over the commercial high pressure ethylenepolymerization processes which apparently require operating pressures inthe range of about 20,000 to about 50,000 p. s. i.

The charging stock to the present polymerization process preferablycomprises essentially ethylene. The ethylene charging stocks may containinert hydrocarbons, as

in refinery gas streams, for example, methane, ethane, propane, etc.However, it is preferred to employ as pure and concentrated ethylenecharging stocks as it is possible to obtain. It is desirable to minimizeor avoid the introduction of oxygen, carbon dioxide, water orsulfurcompounds into contact with the catalyst.

The contact time or space velocity employed in the polymerizationprocess will be selected with reference to the other variables,catalysts, the specific type of product desired and the extent ofethylene conversion desired in any given run or pass over the catalyst.In general, this variable is readily adjustable to obtain the desiredresults. In operations in which the olefin charging stock is caused toflow continuously into and out of contact with the solid catalyst,suitable liquid hourly space velocities are usually selected betweenabout 0.1 and about 10 volumes, preferably about 0.5 to 5 or about 2volumes of olefin solution in a liquid reaction medium, which is usuallyan aromatic hydrocarbon such as benzene or xylenes; tetralin or othercycloaliphatic hydrocarbon, such as cyclohexane or decalin(decahydronaphthalene).

The amount of the ethylene in such solution may be in the range of about2 to 50% by weight, preferably about 2 to about 10 weight percent or,for example, about 5 to 10 weight percent. When the ethyleneconcentration in the liquid reaction medium is decreased below about 2weight percent, the molecular weight and melt viscosity of the polymericproducts tend to dropsharply. In general, the rate of ethylenepolymerization tends to increase with increasing concentration of theethylene in the liquid reaction medium. However, the rate of ethylenepolymerization to form high molecular Weight, normally solid polymers ispreferably not such as to yield said solid polymers in quantities whichsubstantially exceed the solubility thereof in said liquid reactionmedium under the reaction conditions, usually up to about 5-7 weightpercent, exclusive of the amounts of polymeric products which areselectively absorbed by the catalyst. Although ethylene concentrationsabove 10 weight percent in the liquid reaction medium may be used,solutions of ethylene polymer above 510% in the reaction medium becomevery viscous and difficult to handle and severe cracking or spalling ofthe catalyst particles or fragments may occur, resulting in catalystcarry-over as fines with the solution of polymerization products andextensive loss of catalyst from the reactor.

In batch operations, operating periods between one-half and about 20hours, usually between about 1 and about 4 hours, are employed and thereaction autoclave is charged with ethylene as the pressure falls as aresult of the olefin conversion reaction.

The olefin charging stocks can be polymerized in the gas phase and inthe absence of a liquid reaction medium by contact with the alkalineearth metals and nickel catalysts. Upon completion of the desiredpolymerization reaction it is then possible to treat the nickel catalystfor the recovery of the solid polymerization products, for example byextraction with suitable solvents. However, in the interests ofobtaining increased rates of olefin conversion and of continuouslyremoving solid conversion products from the catalyst, it is muchpreferred to effect the conversion of the olefin in the presence ofsuitable liquid reaction media. The liquid reaction medium may also beemployed as a means of contacting the olefin with catalyst by preparinga solution of the olefin feed stock in the liquid reaction medium andcontacting the resultant solution with the polymerization catalyst.

The liquid reaction medium functions as a solvent to remove some of thenormally solid product from the catalyst surface.

Various classes of hydrocarbons or their mixtures which are liquid andsubstantially inert under the polymerization conditions of the presentprocess can be employed. Members of the aromatic hydrocarbon series,particularly the mononuclear aromatic hydrocarbons, viz., benzene,toluene, xylenes, mesitylene and xylene-p-cymene mixtures can beemployed. Tetrahydronaphthalene can also be employed. In addition, wemay employ such aromatic hydrocarbons as ethylbenzene, isopropylbenzene,sec-butylbenzene, t-butylbenzene, ethyltoluene, ethylxylenes,hemimellitene, pseudocurnene, prehnitene, isodurene, diethylbenzenes,isoamylbenzene and the like. Suitable aromatic hydrocarbon fractions canbe obtained by the selective extraction of aromatic naphthas, fromhydroforming operations as distillates or bottoms, from cycle stockfractions of cracking operations, etc.

We may also employ certain alkyl naphthalenes which are liquid under thepolymerization reaction conditions, for example, l-methylnaphthalene,2-isopropylnaphthalene, l-n-amylnaphthalene and the like, orcommercially produced fractions containing these hydrocarbons.

Certain classes of aliphatic hydrocarbons can also be employed as aliquid hydrocarbon reaction medium in the present process. Thus, we mayemploy various saturated hydrocarbons (alkanes and cycloalkanes) whichare liquid under the polymerization reaction conditions and which do notcrack substantially under the reaction conditions. Either pure alkanesor cycloalkanes or commercially available mixtures, freed of catalystpoisons, may be employed. For example, we may employ straight runnaphthas or kerosenes containing alkanes and cycloalkanes. Specifically,we may employ liquid or liquefied alkanes such as n-pentane, n-hexane,2,3-dimethylbutane, n-octane, iso-octane, (2,2,4-trimethylpentane),n-decane, n-dodecane, cyclohexane, methylcyclohexane,dimethylcyclopentane, ethylcyclohexane, decalin, methyldecalins,

dimethyldecalins and the like.

We may also employ a liquid hydrocarbon reaction medium comprisingliquid olefins, e. g., n-hexenes, cyclohexene, octenes, hexadecenes andthe like.

The normally solid polymerization products which are retained on thecatalyst surface or grease-like ethylene polymers may themselvesfunction to some extent as a liquefied hydrocarbon reaction medium, butit is highly desirable to add a viscosity-reducing hydrocarbon, such asthose mentioned above, thereto in the reaction zone.

The liquid hydrocarbon reaction medium should be freed of poisons beforeuse in the present invention by acid treatment, e. g., with anhydrousp-toluenesulfonic acid, sulfuric acid, or by equivalent treatments, forexample with aluminum halides, or other Friedel-Crafts catalysts, maleicanhydride, calcium, calcium hydride, sodium or other alkali metals,alkali metal hydrides, lithium aluminum hydride, hydrogen andhydrogenation catalysts (hydrofining) filtration through a column ofcopper grains or 8th group metal, etc., or by combinations of suchtreatments.

We have purified C. P. xylenes by refluxing with a mixture of 8 weightpercent M003 on A1203 catalyst and LiAlHr (50 cc. xylene--1 g.catalyst-0.2 g. LiAlH4) at atmospheric pressure, followed bydistillation of the xylenes. Still more effective purification ofsolvent can be achieved by heating it to about 225250 C. with eithersodium and hydrogen or NaH plus 8 weight percent Moos-A1203 catalyst ina pressure vessel.

Temperature control during the course of the ethylene conversion processcan be readily accomplished owing to the presence in the reaction zoneof a large liquid mass having relatively high heat capacity. The. liquidhydrocarbon reaction medium can be cooled by heat exchange inside oroutside the reaction zone.

When solvents such as xylenes are employed some slight alkylationthereof by ethylene can occur under the reaction conditions. Thealkylate is removed with grease in the present process, can be separatedtherefrom by fractional distillation and can, if desired, be returned tothe polymerization zone.

The following specific examples are introduced in order to illustratebut not unduly to limit our invention. The exemplary operations wereeffected in 250 cc. capacity stainless steel pressure vessels providedwith a magnetically-actuated stirring device which was reciprocatedthrough the liquid in the vessel in order to obtain good contacting ofthe ethylene and catalyst components.

Example 1 The autoclave was charged with 100 cc. of dehydrated anddecarbonated toluene which was freshly distilled, 1 g. of calcium powderand l g. of nickel catalyst. This catalyst was prepared by evaporating a10% nickel nitrate solution while stirring an activated coconutcharcoal, 8-14 mesh per inch, until all the nickel nitrate was depositedon the support. The catalyst was dried at 110 C. and then heated insteam at atmospheric pressure while the temperature was gradually raisedfrom 100 C. to 290 C. Decomposition of the nickel nitrate on thecharcoal occurred to form a catalyst comprising essentially NiO oncharcoal. The contents of the autoclave were heated with stirring to 153C. while maintaining a partial pressure of 200 p. s. i. of hydrogen andethylene was then injected to a partial pressure of 865 p. s. i.Reaction was continued for hours. Upon conclusion of the reaction thereactor contents were cooled to room temperature, the pressure wasvented to atmospheric pressure and the nickel catalyst containingadsorbed polyethylenes was removed and extracted with hot xylenes. Thehot xylenes solution was cooled to room temperature to precipitate atough, resinous ethylene polymer which was filtered and the filtrate wasevaporated to leave a grease-like solid of polyethylene residue. Thereaction yielded 3.3 g per g. of the nickel catalyst of a solid polymerof ethylene having a specific gravity (24/ 4 C.) f

of 0.955, Williams plasticity of 17.0 and melt viscosity of 1x10 (methodof Dienes and Klemm, J. Appl. Phys. 17, 458-71 (1946)). The yield ofsolid grease-like polyethylenes was 1.65 g. per g. of the nickelcatalyst.

. In sharp contrast to the above results are the results which wereobtained in the following experiment in which no promoter was employed.The charge to the reactor was the same as in theabove example but nopromoter was included and it was found that the yield of solidpolyethylenes was only 0.01 g. per g. and the yield of solid grease-likepolyethylenes was only 0.05 g. per g. of the solid catalyst. Thereaction period, as before, was 20 hours.

In another control run the reactor was charged with 100 cc. of thepurified toluene, 2 g. of the 5% nickel oxide-charcoal catalyst, heatedwith stirring to 131 C. and then pressured with ethylene to a partialpressure of 910 p. s. i. The operating period was 20.5 hours. Thereaction yielded only a trace of solid polyethylenes and 0.25 cc. of aliquid polymer per gram of the nickel catalyst.

Example 2 The reactor was chargedwith 100 cc. of purified toluene, 1 g.of barium chips and 1 g. of nickel catalyst having the same compositionand prepared by the same method as the nickel catalyst of Example 1. Thecontents of the reactor were heated with stirring to 150 C. and ethylenewas then introduced to a partial pressure of 830 p. s. i. Reaction wascontinued for 21 hours. The reaction products were worked up as inExample 1. The yield of solid polyethylenes was 1.68 g. per g. ofni'ckelcatalyst. The high molecular weight solid polyethylenes had aspecific gravity (24/4 C.) of 0.955 and melt'viscosityof 4.7 l0 Thereaction also yielded 1 g. of solid grease-like polyethylenes per gramof the nickel catalyst.

Example 3 The process of Example 1 is repeated but the calcium isreplaced by 2.2 g. of strontium. The products are worked up as before toproduce solid polymers of ethylene.

Example 4 The process of Example 1 is repeated but the calcium isreplaced by about 0.75 g. of magnesium. The products are worked up as inExample 1 to separate solid polyethylenes produced by the process.

In large scale operations the flow-scheme shown in the E. Field and M.Feller application, Serial No. 324,612, filed December 6, 1952, may beemployed. It should be noted that the higher molecular weightpolyethylenes produced in our process are selectively adsorbed by thenickel catalyst and may be removed therefrom by solvent extraction.

The polymers produced by the process of this invention can be subjectedto such after-treatment as may be desired, to fit them forparticularuses or to impart desired properties. Thus, the polymers canbe extruded, mechanically milled, filmed or cast, or converted tosponges or latices. Antioxidants, stabilizers, fillers, extenders,plasticizers, pigments, insecticides, fungicides, etc. can beincorporated in the polyethylenes and/ or in byproduct alkylates orgreases. The polyethylenes may be employed as coating materials,binders, etc.

The polymers produced by the process of the present invention,especially the polymers having high specific viscosities, can be blendedwith the lower molecular weight polyethylenes to impart stiffness orflexibility or other desired properties thereto. The solid resinousproducts produced by the process of the present invention can, likewise,be blended in any desired proportions with hydrocarbon oils, waxes suchas parafiin or petrolatum waxes, with ester waxes, with high molecularweight polybutylenes, and with other organic materials. Smallproportions between about .01 and about 1 percent of the variouspolymers of ethylene produced by the process of the present inventioncan be dissolved or dispersed in hydrocarbon lubricating oils toincrease V. I. and to decrease oil consumption when the compounded oilsare' employed in motors; larger amounts of polyethylenes may 7 becompounded with oils of various kinds and for various purposes.

The products having a molecular weight of 50,000 or more produced by thepresent invention, can be employed in small proportions to substantiallyincrease the ethylene polymer, which process comprises contactingethylene with an alkaline earth metal and a catalyst comprisingessentially a minor proportion of nickel oxide supported upon a majorproportion of an active carbon ata temperature between about 25 C. andabout 250 C., and separating a normally solid ethylene polymer thusproduced.

2. A process for the preparation of a normally solid ethylene polymer,which (process comprises contacting ethylene with an alkaline earthmetal and a catalyst comprising essentially a minor proportion of nickeloxide supported upon a major proportion of an active carbon in thepresence of a liquid hydrocarbon reaction medium at a temperaturebetween about 25 C. and about 250 C., and separating a normally solidethylene polymer thus produced.

3. The process of claim 2 wherein said catalyst comprises between about0.1 and about 20 weight percent nickel.

4. The process of claim 2 wherein said alkaline earth metal is calcium.

5. The process of claim 2 wherein said alkaline earth 7, The process ofclaim 2 wherein said alkaline earth metal "is magnesium? 8. The processof claim 2 wherein said medium is an aromatic hydrocarbon. r i

9. A process for the preparation of a normally solid ethylene polymer,which process comprises contacting ethyleneand a liquid hydrocarbonreaction-medium at a temperature between about 25 C. and about 250 C.under an ethylene partial pressure of at least about 15 p. s. i. with analkaline earth metal and a catalyst comprising essentially nickel oxidein a proportion between about 3 and about 10 weight percent, calculatedas elemental nickel, supported upon an active carbon, the weight ratioof said alkaline earth metal to said nickel catalyst being-between about0.01 and about 10, and separating a normally solid ethylene polymer thusproduced.

10. The process of claim 9 wherein the weight ratio of the alkalineearth metal to the nickel catalyst is between about 0.5 and about 2.

11. The process for the preparation of a resinous ethylene polymer,which process comprises contacting ethylene and a low boiling aromatichydrocarbon reaction medium' at a temperature between about C. and aboutC. under an ethylene partial pressure of at leastabout 500 p. s. i.,with an alkaline earth metal and a catalyst comprising essentially aminor proportion of nickel oxide supported upon a major proportion of anactivated coconut charcoal, the weight ratio of said alkaline earthmetal to said nickel catalyst being between about 0.5 and about 2, andseparating a resinous ethylene polymer thus produced.

12. The process of claim 9 wherein said alkaline earth metal is calcium.

13. The process of claim 9 wherein said alkaline earth metal is barium.

14. The process of claim 9 wherein said alkalineearth v metal isstrontium.

15. The process of claim 9 wherein said alkaline earth metal ismagnesium.

References Cited in the file of this patent UNITED STATES PATENTS

1. A PROCESS FOR THE PREPARATION OF A NORMALLY SOLID ETHYLENE POLYMER,WHICH PROCESS COMPRISES CONTACTING ETHYLENE WITH AN ALKALINE EARTH METALAND A CATALYST COMPRISING ESSENTIALLY A MINOR PROPORTION OF NICKEL OXIDESUPPORTED UPON A MAJOR PROPORTION OF AN ACTIVE CARBON AT A TEMPERATUREBETWEEN ABOUT 25*C. AND ABOUT 250* C., AND SEPARATING A NORMALLYSOLIDETHYLENE POLYMER THUS PRODUCED.